In electromechanical systems, switches provide the function of making and breaking electrical contacts and consequently electrical circuits. In certain system applications, there is a need to employ a switch that is capable of breaking and making electrical contact in circuits that control and/or power equipment. The equipment is desired to have an automatic electrical disconnect installed into the operating circuitry so that upon the occurrence of a selected condition, the circuit can be de-energized.
One type of switch is a limit switch which is a device that serves the function of connecting and disconnecting circuits in a fashion that is related to a given set of inputs. The inputs typically are mechanically derived positions that are linked to the device that is being protected by the limit switch. For example, when a device has reached a point of travel in a particular direction, the limit switch is activated to disconnect the electrical circuit usually stopping the mechanical motion of the device. In this fashion the limit switch limits the degree of travel or motion of the device and so can protect the device.
If a spring is broken in such a switch and no longer provides a bias, then contacts will not be opened upon actuation. Additionally if the contacts become welded perhaps from arcing across the contacts in the circuit, the spring bias may not be capable of opening the contacts. The circuit will remain energized even though the limit switch has been positioned to release the contacts. A spring failure or a stuck contact will prevent the contacts from opening. Damage to the equipment may result.
Electrical circuits are controllable in electromechanical systems through limit switches. Limit switches can open and close electrical circuits to protect equipment. A limit switch is disclosed comprising a housing, a prime contactor and an adjustment contactor disposed within the housing. The prime contactor and the adjustment contactor are electrically coupled in series. A plunger is disposed in the housing. The prime contactor is openable by the plunger, and the adjustment contactor is closable by the plunger. A redundant prime contactor and a redundant adjustment contactor are also disposed within the housing. The redundant adjustment contactor is electrically coupled in series with the redundant prime contactor. The redundant prime contactor is openable by the plunger, and the redundant adjustment contactor is closable by the plunger. An actuator is in operable communication with the plunger.
A method of controlling a circuit with a limit switch is disclosed comprising aligning the limit switch in a mid-position alignment. The circuit is controlled with the limit switch by actuating the limit switch by direct acting contact by a plunger against a prime contactor. Opening the prime contactor, or opening the redundant prime contactor, de-energizes the electrical circuit of the limit switch. Closing the prime contactor along with the redundant prime contactor while the adjustment contactor and the redundant adjustment contactor is maintained closed, can be done to energize the electrical circuit. Opening the adjustment contactor or the redundant adjustment contactor when an actuator is misaligned from the plunger can be completed to de-energize the electrical circuit.
The above described and other features and advantages of the invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and claims.